1. Field of the Invention
The invention relates to fire suppression compositions, and more particularly to fire suppression compositions that are environmentally innocuous, and that act both physically and chemically to extinguish fires.
2. Brief Description of the Art
Halogen-containing agents, such as Halon 1211 (bromochlorodifluoromethane, CF.sub.2 BrCl) and Halon 1301 (trifluorobromomethane, CF.sub.3 Br) have been utilized as effective fire suppression agents for many years. These fire suppression agents generate chemically reactive halogen radicals which interfere with the combustion process, and provide an important advantage to the fire extinguishing capability of Halons. However, certain halogen-containing fire suppression agents, such as Halon-1301, contribute significantly to the destruction of stratospheric ozone in the atmosphere. Halon 1301 is a volatile compound and upon high altitude photolysis, Halon 1301 forms reactive chemical radicals that react with ozone (O.sub.3) to produce oxygen (O.sub.2).
CF.sub.3 Br+h.nu..fwdarw.CF.sub.3.+Br. PA1 Br.+O.sub.3 .fwdarw.BrO.+O.sub.2 PA1 BrO.+O.sub.3 .fwdarw.Br.+2 O.sub.2
In order to reduce stratospheric ozone depletion caused by Halons, nearly all commercially available fire suppression agents that are designed today are "physically acting" agents. In other words, these fire suppression agents use physical properties rather than chemical properties to suppress fires. Examples of physically-acting fire suppression agents include inert gases such as carbon dioxide (CO.sub.2), water vapor (H.sub.2 O) and nitrogen (N.sub.2). When applied to a fire, these inert gases is physically displace oxygen from the combustion region while simultaneously serving as a heat sink to reduce the temperature of the combustion zone. The combination of these two physical actions results in extinction of the fire. An example of this type of fire suppression agent is U.S. Pat. No. 5,423,384, to Galbraith et al. which describes an apparatus that delivers liquid and solid fire suppression agents such as water vapor, carbon dioxide, and nitrogen gas.
Unfortunately, physically-acting fire suppression agents are less efficient than chemically-acting fire suppression agents. Accordingly, larger quantities of physicially-acting fire suppressant are required in order to extinguish fires. Consequently, bulky equipment and larger storage containers must frequently be used in conjunction with physically-acting fire suppression agents. The bulky nature of this equipment is a disadvantage in certain applications where space is limited, such as military or civilian aircraft or ground vehicle engine bays, spacecraft, or military or civilian aircraft drybays.
Solid propellant formulations similar to those used in rocket engines and automotive airbags have recently found new applications as physically-acting fire suppression agents. The gases formed from solid propellant-based fire suppression agents As offer advantages such as low ozone depletion potential (ODP), and low environmental impact. For example, solid propellant compositions based on sodium azide fuel and inorganic oxidizers generate nearly pure inert nitrogen gas. Similarly, azide-free formulations offer improved efficiencies for production of large volumes of chemically inert gas mixtures with minimal levels of noxious gases. In addition to these advantages, solid propellants are capable of generating large amounts of chemically inert gases (mainly CO.sub.2, N.sub.2, H.sub.2 O) from relatively small amounts of solid materials. Thus, the effective storage density for such fire suppression agents is high. However, as indicated above, such systems generally suffer from reduced efficiency due to heavy reliance upon physical fire suppression activity rather than the more efficient chemical fire suppression activity.
Additional fire extinguishing materials and methods are known in the art, many of which are directed to physical methods of extinguishing fires. For example, U.S. Pat. No. 4,601,344 to Reed et al. describes a fire extinguishing method that utilizes a gas generating composition comprising glycidyl azide polymer and a high nitrogen content solid additive, such as guanylaminotetrazole nitrate, bis(triaminoguanidium)-5,5'-azotetrazole, ammonium 5-nitroaminotetrazole, and high bulk density nitroguanidine.
U.S. Pat. No. 5,520,826 to Reed et al. discloses a fire extinguishing method that utilizes a gas generating composition comprising glycidyl azide polymer, an azido plasticizer, a high nitrogen content solid additive, and the potassium salt of perfluorooctanoic acid. Aromatic bromine additives may be added to the composition as a chemical fire suppressant; however, such additives are hazardous to human health and the environment.
U.S. Pat. No. 5,423,385 to Baratov et al. describes formulations of fire extinguishing aerosols which include an oxidant and a reducing agent. The compositions of these aerosols extinguish fires using a combination of heat absorption and chemical interaction.
U.S. Pat. No. 3,972,820 to Filter et al. describes a fire extinguishing composition that comprises a halogen-containing fire extinguishing agent, an oxidizer, and a binder. However, the organic species that are generated are typically considered carcinogenic and environmental health hazards.
Accordingly, what is needed in the art is a fire suppression composition that provides the benefits of both physical fire suppression and chemical fire suppression, and that is environmentally innocuous. The present invention is believed to be an answer to that need.